The present invention relates generally to wireless telecommunications, and specifically to advanced cellular telephone networks.
The Global System for Mobile (GSM) telecommunications is used in cellular telephone networks in many countries around the world. GSM offers a useful range of network services and standards. GSM standards define protocol stacks that are used in conveying signaling and user traffic between elements of the network, including subscriber units (also known as mobile stationsxe2x80x94MSs), base station subsystems (BSSs) and mobile switching centers (MSCs).
FIG. 1 is a block diagram schematically illustrating the GSM standard protocol stack used in signaling over dedicated control channels between an MS and the network, as is known in the art and defined by GSM standards, particularly the GSM 04.xx series of standards. The term xe2x80x9cdedicatedxe2x80x9d refers to communication channels used during a call to or from the MS, as opposed to when the MS is in an idle, or standby, state. The lowest protocol layer is the physical layer of the air interface, which in existing GSM networks is based on time-division multiple access (TDMA) digital communications technology. The data link layer provides data link services and functionality, as defined in particular in GSM standards 04.05 and 04.06, which are incorporated herein by reference. The GSM data link layer supports both acknowledged and unacknowledged messaging operation modes. In the acknowledged mode, the data link layer provides reliable transmission of upper layer messages, with services including: (1) message ordering, (2) priority and fragmentation, and (3) suspension and resumption of communications.
A radio interface layer, which in one embodiment includes three sublayers, controls and passes signals through the data link layer and physical layer. It will be understood by those skilled in the art that the terms Layer 1 and physical layer are commonly used interchangeably. Similarly, Layer 2 and the data link layer are commonly used interchangeably. Furthermore, the terms Layer 3, RIL3, and radio interface layer are commonly used interchangeably by those skilled in the art. In the present case, the terms physical layer, data link layer, and radio interface layer are used throughout, merely for the sake of clarity.
The lowest sublayer of the radio interface layer is a Radio Resource (RR) management sublayer. The RR management sublayer supports Mobility Management (MM) and Call Management (CM) sublayers above it. The CM sublayer supports signaling for call processing, as well as GSM supplementary services. The MM sublayer supports signaling required for locating the MS, authentication and encryption key management. It should be noted that any protocol that may be used to transmit messages through the physical layer and the data link layers, such as protocols associated with GSM short message service (SMS), would be considered to be a radio interface layer protocol for the purpose of this description.
Code-division multiple access (CDMA) is an improved digital communications technology, which affords more efficient use of radio bandwidth than TDMA, as well as a more reliable, fade-free link between cellular telephone subscribers and base stations. The leading CDMA standard is TIA/EIA-95 (commonly referred to as IS-95), promulgated by the Telecommunications Industry Association (TIA). IS-95 defines its own protocol stack for transmission of signaling over traffic channels, including a physical layer and a data link layer. Because the IS-95 CDMA air interface is based on fundamentally different technology from the GSM TDMA interface, there are substantial differences between the conventional IS-95 and GSM protocol stacks. Furthermore, the standard IS-95 data link layer does not provide some of the data link layer services defined by GSM standards for signaling over traffic channels, particularly services associated with acknowledged mode operation. For example, IS-95 data link layer does comply with GSM requirements for signaling on overhead (e.g., paging and access) channels.
International Patent Application Number PCT/US96/20764, which is incorporated herein by reference, describes a wireless telecommunications system that uses a CDMA air interface to implement GSM network services and protocols. Using this system, at least some of the TDMA base stations and subscriber units of an existing GSM network would be replaced or supplemented by corresponding CDMA equipment. CDMA BSSs (base station subsystems) in this system are adapted to communicate with GSM mobile switching centers (MSCs) via a standard GSM A-interface. Core GSM network services are thus maintained, and the changeover from TDMA to CDMA is transparent to users.
Hybrid cellular communications networks, incorporating both GSM and CDMA elements, are also described in International Publication Numbers WO 95/24771 and WO 96/21999, and in an article by Tscha, et al., entitled xe2x80x9cA Subscriber Signaling Gateway between CDMA Mobile Station and GSM Mobile Switching Center,xe2x80x9d in Proceedings of the 2nd International Conference on Universal Personal Communications, Ottawa (1993), pp. 181-185, which are incorporated herein by reference.
It is an object of some aspects of the present invention to provide methods and apparatus for conveying signaling over dedicated channels of an air interface between mobile stations and base station subsystems in a hybrid Global System for Mobile (GSM)/Code Division Multiple Access (CDMA) cellular communications network.
It is a further object of some aspects of the present invention to provide communications protocols that enable the use of GSM-compatible signaling over dedicated channels of a CDMA air interface.
In preferred embodiments of the present invention, a mixed GSM/CDMA cellular communications system includes one or more CDMA base station subsystems (BSSs), controlled by a GSM mobile switching center (MSC). A mobile station (MS) and one of the BSSs communicate over a CDMA air interface (i.e., physical layer) using a protocol stack including a data link layer that is modified so as to support a GSM-CDMA radio interface layer that is based on a GSM radio interface layer. Preferably, at least the Radio Resource (RR) sublayer of the GSM radio interface layer is also modified so as to interact with the CDMA air interface (i.e., physical layer), as described further in a U.S. patent application Ser. No. 09/119,717, entitled xe2x80x9cBase Station Handover in a Hybrid GSM/CDMA Network,xe2x80x9d filed Jul. 20, 1998, which is assigned to the assignee of the present patent application and is incorporated herein by reference. This modified RR is referred to as a GSM-CDMA RR.
The system thus enables the use of GSM signaling in dedicated traffic channels over the CDMA air interface. The modifications to the protocol stack provide functionality required to support substantially all of the GSM dedicated channel signaling services that are not provided by CDMA communications industry standards.
In some preferred embodiments of the present invention, the mixed GSM/CDMA cellular communications system includes both TDMA and CDMA base stations, jointly controlled by a mobile switching center (MSC). Systems of this type are described generally in the above-mentioned international applications and the above referenced U.S. patent application entitled xe2x80x9cBase Station Handover in a Hybrid GSM/CDMA Networkxe2x80x9d. The MS is capable of communicating with both types of base stations, by appropriately switching between TDMA and CDMA air interfaces, while preferably using GSM network and signaling protocols over both types of interface. This use of GSM protocols over the CDMA air interface is enabled by the modified data link layer and by suitable modification of the GSM-RR sublayer. The Mobility Management (MM) and Call Management (CM) sublayers are preferably substantially unmodified relative to GSM standards.
In some preferred embodiments of the present invention, the modified data link layer comprises two sublayers: a lower sublayer, substantially corresponding to IS-95 data link layer, as defined by the IS-95 specification, which communicates with the CDMA physical layer; and an upper sublayer, referred to herein as an adaptation sublayer, communicating between the lower sublayer and the RR sublayer of the GSM-CDMA radio interface layer. The adaptation sublayer provides additional functionality that is required by GSM standards relating to data link layer, but is not offered by the lower sublayer (i.e., by IS-95 data link layer). The additional functionality preferably includes: (1) procedures for provisioning several data links, each having different transmission properties; (2) identification of data link connection endpoints; (3) ordering of radio interface layer messages; (4) fragmentation and re-assembly of large radio interface layer messages; (5) transmission of radio interface layer messages according to their priority; (6) suspension and resumption of data link services during handover; and (7) transparent transmission of IS-95 signaling messages (tunneling).
There is therefore provided, in accordance with a preferred embodiment of the present invention, in a GSM mobile wireless telecommunications system, a method for conveying signaling between a mobile station and a base station via a CDMA air interface, including:
generating a signaling message based on a GSM interface standard;
providing data link services to process the message for transmission over the CDMA air interface; and
transmitting the processed message over the CDMA air interface.
Preferably, providing the data link services includes producing an IS-95 message for transmission, using a data link layer to process the signaling message based on the GSM interface standard. The data link layer preferably includes an adaptation sublayer, which receives and, most preferably, encapsulates the signaling message to produce the IS-95 message based on the signaling message.
Additionally or alternatively, the inventive data link layer further includes an IS-95 data link layer, and the adaptation sublayer receives the signaling message from a radio resource protocol sublayer based on a GSM standard conveys the IS-95 message to the IS-95 data link layer. Preferably, the adaptation sublayer further receives a signaling message based on an IS-95 standard and conveys the message based on the IS-95 standard to the data link layer substantially without processing.
Preferably, providing the data link services includes encapsulating the message, most preferably in the general form of an IS-95 Data Burst Message.
In a preferred embodiment, providing the data link services includes fragmenting the message into a plurality of sub-messages for transmission over the CDMA air interface. Preferably, fragmenting the message includes assigning a message number in a header of each of the sub-messages according to a sequential order thereof, and the method includes receiving the sub-messages and concatenating them in the sequential order responsive to the message number.
Preferably, generating the message includes generating a plurality of messages having an assigned order, and the method includes receiving the messages in an acknowledged operation mode over the CDMA air interface and arranging the messages responsive to the assigned order.
Further preferably, generating the message includes generating a plurality of messages having respective priorities, and providing the data link services includes conveying the processed messages for transmission over the CDMA air interface in an order responsive to the priorities thereof, wherein providing the data link services preferably includes assigning a priority responsive to a GSM service access point indicator.
Preferably, providing the data link services includes suspending transmission of messages by the mobile station during a hard handover of the mobile station from a first base station to a second base station and resuming the transmission after the handover is complete. In a preferred embodiment, the first base station has a CDMA air interface, and the second base station has a GSM-TDMA air interface, and providing the data link services includes transferring the messages whose transmission is suspended responsive to the hard handover to a GSM data link layer, so that the message is prepared for transmission over the GSM-TDMA air interface.
Preferably, transmitting the processed message includes transmitting a message over a traffic channel.
There is further provided, in accordance with a preferred embodiment of the present invention, wireless communications apparatus, for use in a GSM mobile telecommunications system, including a base station and a mobile station, which communicate over a CDMA air interface and provide data link services for processing of messages to be transmitted over the CDMA air interface, such that signaling messages between the base station and the mobile station, which are generated in accordance with a GSM interface standard, are processed for transmission using the data link services, whereby the signaling messages are transmitted over the CDMA air interface.
Preferably, the CDMA air interface is based on an IS-95 standard, wherein the base station and mobile station communicate using a protocol stack including a data link layer to process the signaling messages based on the GSM interface standard. The data link layer preferably includes an adaptation sublayer that receives and, most preferably, encapsulates the signaling message and produces the IS-95 message based on the signaling message.
In a preferred embodiment, the data link layer further includes an IS-95 data link layer, and the adaptation sublayer receives the signaling message from a radio resource protocol sublayer based on a GSM standard and conveys the IS-95 message to the IS-95 data link layer. Preferably, the adaptation sublayer further receives a signaling message based on an IS-95 standard and conveys the message based on the IS-95 standard to the data link layer substantially without processing. Further preferably, the signaling messages are encapsulated for transmission, most preferably in the general form of IS-95 Data Burst Messages.
Preferably, at least some of the messages are fragmented into a plurality of sub-messages for transmission over the CDMA air interface, wherein a message number is assigned in a header of each of the sub-messages according to a sequential order thereof, and when the sub-messages are received, they are concatenated in the sequential order responsive to the message number.
In a preferred embodiment, a plurality of messages are transmitted according to an assigned order in an acknowledged transmission mode over the CDMA air interface, and when the messages are received, they are arranged for output responsive to the assigned order.
Preferably, the messages have respective priorities and are conveyed for transmission over the CDMA air interface in an order responsive to the priorities thereof, wherein the priorities are assigned responsive to a GSM service access point indicator.
Preferably, the mobile station suspends transmission of the messages during hard handover of the mobile station from a first base station to a second base station and resumes transmission after the handover is complete. In a preferred embodiment, the first base station has a CDMA air interface, and the second base station has a GSM-TDMA air interface, wherein suspended messages are transferred responsive to the handover to a GSM data link layer, so that the message is prepared for transmission over the GSM-TDMA air interface. Preferably, the processed message is transmitted over a traffic channel.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: